It is known to provide a roller with a journaling assembly which is capable of measuring the stress applied thereto by a web or strip of material passing over this roller. Such a device or apparatus can include a measuring ring readily supported in a support ring and receiving, in an opening of this measuring ring, the bearings whereby the roller is journaled in a journal block or other support assembly for the roller. The journal block can hold the support ring. Deformation of the measuring ring can be measured, e.g. by a strain gauge, and the force supplied by the web to the measuring ring can thereby be detected and translated into the tensile stress applied to the web.
Such measuring devices can be used in lines, processes and installations for the treatment or manufacture of paper, synthetic resin (plastic), metal or composite material webs. In all such processes and installations, whether they are utilized for coating, treating, shaping or otherwise modifying some property of the material, the web is generally displaced along a transport path and it is important to monitor the stretch of the web or the tensile stress applied thereto so that critical maximum stresses are not applied and, as such stresses are approached, the tensile stress is reduced.
Monitoring systems with this in view are utilized to reduce damage to the web and avoid interruption of the operation of the plant or damage to the equipment or machinery. Obviously, operating costs can be reduced when standstill is avoided by appropriate monitoring of the tensile stress and the prevention of overstressing of the web.
The stretch or tensile stress applied to the web can be monitored by devices of the type described and these devices can be used to generate signals which may be utilized to operate a brake controlling the drag or the drive or control mechanism applying the tractive force to the web or assembly to produce an alarm which signals the approach to a critical threshold of such tensile stress which should not be exceeded.
For example, there is in use the ELMESS web tension measuring device produced by Erhardt & Leimer GmbH, 8900 Augsburg 1, Germany, wherein in at least one journal block of the shaft of a deflection roller for the web a measuring ring assembly is provided of the aforedescribed type.
While this assembly operates effectively, it frequently requires more space than may be available; indeed, in some cases, and this may be its most significant detriment, it may not be capable of achieving sufficient accuracy because of inadequate sensitivity to minor fluctuations in the tensile force applied to the web.
In German laid-open application DE-OS No. 24 09 372, a linear force measuring system is described in which the measuring ring has a measuring segment constituted by two semicircular slits with linearly extended end regions that extend beyond the ends of the semicircle. The measuring zones are the zones between these linear extensions of the semicircular slits and are comparatively narrow or short and have approximately a square configuration or outline. The strain gauges are applied to these zones which deform comparatively slightly so that, when force is applied to the roller by the web, the deformation at these zones sensed by the strain gauges is comparatively little or, put otherwise, the force applied to the roller and hence the tensile stress applied to the web, must be considerable before the deformation of the aforementioned zones of the measuring ring is sufficient to provide significant values to the change in the electrical properties of the strain gauge strips.
As a consequence, this earlier system is likewise insufficiently precise or sensitive to especially small changes in the web traction.
The earlier device, as the German application will reveal, also required axial cutouts which were costly to fabricate, these recesses being necessary to increase the yieldability of the deformation zone. Finally, the arcuate slits which were required in the measuring ring were difficult and expensive to fabricate with accuracy.